Field of the Invention
The present invention relates to the technical field of crop protection by using ALS (acetolactate synthase; also known as AHAS (acetohydroxyacid synthase; EC 2.2.1.6; formerly EC 4.1.3.18)) inhibitor herbicides against unwanted vegetation in areas of growing Beta vulgaris plants, preferably sugar beet, that are tolerant against ALS inhibitor herbicides by comprising mutations in the endogenous ALS gene thereby encoding an ALS polypeptide having an amino acid that is different from the naturally occurring tryptophan (i.e. the tryptophan of the wild-type ALS protein) at position 569 and having an amino acid that is different from the naturally occurring proline (i.e. the proline of the wild-type ALS protein) at position 188.
Description of Related Art
Thus, the mutated sugar beet plants used in the context of the present invention comprise mutations in the ALS gene where the tryptophan at position 569 in the encoded ALS enzyme (corresponding to position 574 in the Arabidopsis thaliana ALS enzyme) is substituted by another amino acid (preferably by leucine), and a mutation in the ALS gene where the proline at position 188 in the encoded ALS enzyme (corresponding to position 197 in Arabidopsis thaliana ALS enzyme) is substituted by another amino acid (preferably by serine).
Cultivated forms of Beta vulgaris (as defined in Ford-Lloyd (2005) Sources of genetic variation, Genus Beta. In: Biancardi E, Campbell L G, Skaracis G N, De Biaggi M (eds) Genetics and Breeding of Sugar Beet. Science Publishers, Enfield (NH), USA, pp 25-33) are important agricultural crops in temperate and subtropical regions. For example, about 20% of the world sugar production is based on sugar beet. Because beet seedlings and juvenile plants during their first 6-8 weeks of their life are susceptible for strong competition caused by fast growing weeds, which outcompete the young crop plants, reliable weed control measures are imperative in these crop areas.
Since more than 40 years, herbicides are the preferred tools to control weeds in sugar beet (Beta vulgaris subsp. vulgaris var altissima). The products used for this purpose, namely phenmedipham, desmediphan, ethofumesate, and metamitron allow to suppress weeds in sugar beet fields without damaging the crop. Nevertheless, under adverse environmental conditions the efficacy of these products leaves room for improvements, especially if noxious weeds like Chenopodium album, Amaranthus retroflexus and/or Fallopia convolvulus germinate over an extended period of time.
The ALS/AHAS enzyme is present in bacteria, fungi, and plants and from various organisms protein isolates have been obtained and their corresponding amino acid/nucleic acid sequences as well as their biochemical characteristics have been determined/characterized (for review, see at Umbarger, H. E., Annu. Rev. Biochem. (1978), 47, 533-606; Chiman, D. M. et al., Biochim Biophys. Acta (1998), 1385, 401-419; Duggleby, R. G., and Pang, S. S., J. Biochem. Mol. Biol. (2000), 33, 1-36; Duggleby, R. G. (Structure and Properties of Acetohydroxyacid Synthase in Thiamine: Catalytic Mechanisms in Normal and Disease States, Vol 11, Marcel Dekker, New York, 2004, 251-274)
The use of herbicidal compounds belonging to the class of ALS inhibitors, like (a) sulfonylurea herbicides (Beyer E. M et al. (1988), Sulfonylureas in Herbicides: Chemistry, Degradation, and Mode of Action; Marcel Dekker, New York, 1988, 117-189), (b) sulfonylaminocarbonyltriazolinone herbicides (Pontzen, R., Pflanz.-Nachrichten Bayer, 2002, 55, 37-52), (c) imidazolinone herbicides (Shaner, D. L., et al., Plant Physiol., 1984, 76, 545-546; Shaner, D. L., and O'Connor, S. L. (Eds.) The Imidazolinone Herbicides, CRC Press, Boca Raton, Fla., 1991), (d) triazolopyrimidine herbicides (Kleschick, W. A. et al., Agric. Food Chem., 1992, 40, 1083-1085), and (e) pyrimidinyl(thio)benzoate herbicides (Shimizu, T. J., Pestic. Sci., 1997, 22, 245-256; Shimizu, T. et al., Acetolactate Syntehase Inhibitors in Herbicide Classes in Development, Boger, P., Wakabayashi. K., Hirai, K., (Eds.), Springer Verlag, Berlin, 2002, 1-41) for the control of unwanted vegetation in various crop cultures is well known in agriculture.
A broad variety of ALS/AHAS inhibitor herbicides enable a farmer to control a wide range of weed species independently of their growth stages, but these highly efficient herbicides cannot be used in Beta vulgaris, preferably sugar beet, because Beta vulgaris, especially conventional sugar beet plants/commercial sugar beet varieties are highly susceptible against/affected by these ALS inhibitor herbicides. Nevertheless, these ALS inhibitor herbicides show an excellent herbicidal activity against broadleaf and grass weed species. The first herbicides based on ALS inhibitors were developed for their use in agriculture already 30 years ago. Nowadays, active ingredients of this class exhibit a strong weed control and are widely used in maize and cereals as well as in dicot crops, except Beta vulgaris, preferably sugar beet.
By now, there is only one commercially available product based on a sulfonylurea herbicide, i.e. Debut® (component (A) 50% triflusulfuron-methyl+component (B) a specific formulation compound, i.e. a specific adjuvant) which can be used in sugar beet in post emergent application, but it requires the application at a very early leaf stage of the weeds to be treated and also show severe gaps in the treatment of serious weeds growing in sugar beet plantings. This sulfonylurea is not tolerated by but degraded in the sugar beet plants.
Another, more reliable and more flexible way to obtain Beta vulgaris, preferably sugar beet plants that stand an ALS inhibitor herbicide treatment is to generate mutants that are sufficiently tolerant to agronomically useful/necessary quantities of ALS inhibitor herbicides in order to control serious unwanted vegetation in Beta vulgaris, preferably sugar beet plantings.
Since ALS inhibitor herbicides were introduced into agriculture it was observed that susceptible plant species, including naturally occurring weeds, occasionally develop spontaneous tolerance to this class of herbicides. Single base pair substitutions at specific sites of the ALS gene usually lead to more or less resistant ALS enzyme variants which show different levels of inhibition by the ALS inhibitor herbicides.
Plants conferring mutant ALS alleles therefore show different levels of tolerance to ALS inhibitor herbicides, depending on the chemical structure of the ALS inhibitor herbicide and the site of the point mutation(s) in the ALS gene and the hereby encoded ALS protein.
Several mutants (naturally occurring in weeds but also artificially induced in crops by either mutation or transgenic approaches) of the ALS conferring tolerance to one or more chemicals defined under the above given ALS inhibitor herbicide classes/groups are known at various parts of the enzyme (i.e. in the α-, β-, and γ-domain of the ALS h are known and have been identified in various organisms, including plants (U.S. Pat. No. 5,378,824; Duggleby, R. G. et al., (2008), Plant Physiol. and Biochem., pp 309-324; Siyuan, T. et al. (2005), Pest Management Sci., 61, pp 246-257; Jung, S. (2004) Biochem J., pp 53-61; Kolkman, J. M. (2004), Theor. Appl. Genet., 109, pp 1147-1159; Duggleby, R. G. et al (2003), Eur. J. Biochem., 270, pp 2895-2904; Pang, S. S., et al. (2003), J. Biol. Chem., pp 7639-7644); Yadav, N. et al., (1986), Proc. Natl. Acad. Sci., 83, pp 4418-4422), Jander G. et al. (2003), Plant Physiol., 131, pp. 139-146); Tranel, P. J., and Wright, T. R. (2002), Weed Science, 50, pp 700-712); Chang, A. K., and Duggleby, R. G. (1998), Biochem J., 333, pp. 765-777).
Crop plants conferring mutant ALS alleles do show different levels of tolerance to ALS inhibitor herbicides, depending on the chemical structure of the ALS inhibitor herbicide and the site of the point mutation in the ALS gene.
For example, Hattori et al. (1995), Mol. Gen. Genet. 246: 419-425, describes a single mutation in the Trp 557 codon in a Brassica napus cell line (according to the numbering of the Arabidopsis thaliana sequence that is used in the literature in order to compare all ALS/AHAS mutants this refers to position “574”)—which equals position 569 of the sugar beet ALS polypeptide sequence. These authors observed resistance to several members of sub-classes of ALS inhibitor herbicides, like sulfonylureas, imidazolinones and triazolopyrimidines.
EP-A-0360750 describes the production of ALS inhibitor herbicide tolerant plants by producing an increased amount of the attacked ALS inside the plant. Such plants show an increased tolerance against certain sulfonyureas, like chlorsulfuron, sulfometuron-methyl, and triasulfuron.
U.S. Pat. No. 5,198,599 describes sulfonylurea and imidazolinone tolerant plants that have been obtained via a selection process and which show a tolerance against chlorsulfuron, bensulfuron, chlorimuron, thifensulfuron and sulfometuron.
Furthermore, U.S. Pat. No. 5,013,659, U.S. Pat. No. 5,141,870, and U.S. Pat. No. 5,378,824 describe the production of transgenic sugar beet plants by introducing a modified yeast ALS gene into such sugar beet plants.
In addition, Saunders et al. (Crop Science, 1992, 32, 1357-1360) disclose sulfonylurea tolerant sugar beet plants that were obtained via somaclonal cell selection but these authors neither showed up any biological data concerning the level of tolerance of such plants against ALS inhibitor herbicide treatment nor did they demonstrate genetically stable mutants obtained from cultures in which these mutations have been generated.
Tan et al. report in Pest Manag. Sci. 2005, 61, 246-257 on weed control in certain imidazolinone-tolerant crops.
Stougaard et al. (1990), J. Cell Biochem., Suppl. 14E, 310 describe the isolation of ALS mutants in a tetraploid sugar beet cell culture. Two different ALS genes (ALS I and ALS II) were isolated which differed at amino acid position 37 only. Mutant 1 contained in its ALS I gene 2 mutations, while mutant 2 contained 3 mutations in its ALS II gene. After the mutations were separated to resolve which mutation would confer resistance against an ALS inhibitor, it was revealed that ALS synthesized from a recombinant E. coli was herbicide resistant if it contained a point mutation in the Trp 574 codon (according to the numbering of the Arabidopsis thaliana sequence that is used in the literature in order to compare all ALS mutants)—which equals position 569 of the beet ALS amino acid sequence, leading to a replacement of the amino acid “Trp” by the amino acid “Leu”. Stougaard et al did not show in sugar beet that the mutation at position 569 of any of the sugar beet ALS genes is sufficient in order to obtain an agronomically acceptable level of tolerance to ALS inhibitor herbicides. Moreover, Stougaard et al did not regenerate or handle sugar beet plants comprising a mutation, including Trp→Leu mutation at position 569 of sugar beet ALS.
Knowing this, Stougaard et al. constructed plant transformation vectors containing different ALS genes for use in plant transformation. However, up to now, no further data—especially not concerning the effects of the application of ALS inhibitor herbicides to plants and/or agricultural areas comprising this mutation in Beta vulgaris plants have been disclosed by these or other authors either in genetically engineered or mutant plants over more than 20 years, thereafter.
Additionally, beet mutants were described conferring a point mutation in the Ala 122 codon which led to a certain tolerance to the ALS inhibitor herbicide subclass of imidazolinones (WO 98/02526) but which is not sufficient for weed control in agricultural application schemes. No cross-tolerance to other ALS inhibitor herbicide classes was described by employing this mutant. Furthermore, beet plants conferring a second point mutation in the Pro 197 codon showed a moderate tolerance to ALS inhibitor herbicides belonging to members of the subclass of sulfonylurea herbicides. Also double mutants of these two were described (WO 98/02527). However, none of these mutants were used for the market introduction of beet varieties because the level of herbicide tolerance to ALS inhibitor herbicides was not sufficiently high in these mutants to be exploited agronomically.
WO 2012/049268 discloses a method for the manufacture of sugar beet plant resistant to several ALS inhibitors, including to foramsulfuron, which comprises the steps of exposing to foramsulfuron calli obtained from explants of B. vulgaris, and regenerating plants from the few spontaneous mutants that can grow in the presence of this herbicide. Said method yielded plants having a mutation in the ALS gene, where the tryptophan at position 569 of the encoded ALS enzyme (corresponding to the 574 position of the Arabidopsis thaliana ALS enzyme) is substituted by a leucine. WO 2012/049266 relates to the use of ALS inhibitor herbicides for control of unwanted vegetation in ALS inhibitor herbicide tolerant Beta vulgaris plants having a mutation in the ALS gene, where the tryptophan at position 569 of the encoded ALS enzyme.
WO 2008/124495 discloses ALS double and triple mutants. According to WO 2009/046334, specific mutations in the ALS gene were provided. However, agronomically exploitable Beta vulgaris mutants containing such mutations according to WO 2009/046334 and also showing a sufficient tolerance to any kind of ALS inhibitor herbicides of various ALS inhibitor herbicide classes have not been obtained/described by now.
All these sugar beet mutants do not show a reliable tolerance and/or do not show satisfactory tolerance against various classes of the ALS inhibitor herbicides, and—even worse—they do not show a tolerance level that is sufficient and useful at agronomic application rates against any kind of ALS inhibitor herbicides.
As it relates to the compounds known acting as ALS inhibitor herbicides, these can be grouped in several classes.
Compounds from the group of the (sulfon)amides are already known as herbicidally active compounds for controlling unwanted vegetation; see, for example, EP 239414, U.S. Pat. No. 4,288,244, DE 3303388, U.S. Pat. No. 5,457,085, U.S. Pat. No. 3,120,434, U.S. Pat. No. 3,480,671, EP 206251, EP 205271, U.S. Pat. No. 2,556,664, U.S. Pat. No. 3,534,098, EP 053011, U.S. Pat. No. 4,385,927, EP 348737, DE 2822155, U.S. Pat. No. 3,894,078, GB 869169, EP 447004, DE 1039779, HU 176582, U.S. Pat. No. 3,442,945, DE 2305495, DE 2648008, DE 2328340, DE 1014380, HU 53483, U.S. Pat. No. 4,802,907, GB 1040541, U.S. Pat. No. 2,903,478, U.S. Pat. No. 3,177,061, U.S. Pat. No. 2,695,225, DE 1567151, GB 574995, DE 1031571, U.S. Pat. No. 3,175,897, JP 1098331, U.S. Pat. No. 2,913,327, WO 83/00329, JP 80127302, DE 1300947, DE 2135768, U.S. Pat. No. 3,175,887, U.S. Pat. No. 3,836,524, JP 85067463, U.S. Pat. No. 3,582,314, U.S. Pat. No. 5,333,0821, EP 131258, U.S. Pat. No. 4,746,353, U.S. Pat. No. 4,420,325, U.S. Pat. No. 4,394,506, U.S. Pat. No. 4,127,405, U.S. Pat. No. 4,479,821, U.S. Pat. No. 5,009,699, EP 136061, EP 324569, EP 184385, WO 02/30921, WO 92/15576, WO 95/29899, U.S. Pat. No. 4,668,277, EP 305939, WO 96/41537, WO 95/10507, EP 007677, CN 01080116, U.S. Pat. No. 4,789,393, EP 971902, U.S. Pat. No. 5,209,771, EP 084020, EP 120814, EP 087780, WO 88/04297, EP 5828924, WO 02/36595, U.S. Pat. No. 5,476,936, WO 2009/053058 and the literature cited in the publications mentioned above.
Compounds from the group of the imidazolinones are already known as herbicidally active compounds for controlling unwanted vegetation; see, for example
Proc. South. Weed Sci. Soc. 1992. 45, 341, Proc. South. Weed Sci. Soc. Annu. Mtg. 36th, 1983, 29, Weed Sci. Soc. Annu. Mtg. 36th, 1983, 90-91, Weed Sci. Soc. Mtg., 1984, 18, Modern Agrochemicals, 2004, 14-15.
Compounds from the group of the pyrimidinyl(thio)benzoates are already known as herbicidally active compounds for controlling unwanted vegetation; see, for example U.S. Pat. No. 4,906,285, EP 658549, U.S. Pat. No. 5,118,339, WO 91/05781, U.S. Pat. No. 4,932,999, and EP 315889.
Compounds from the group of the sulfonanilides are already known as herbicidally active compounds for controlling unwanted vegetation; see, for example WO 93/09099, WO 2006/008159, and WO 2005/096818.
All publications and patents cited in this disclosure are incorporated by reference in their entirety. To the extent the material incorporated by reference contradicts or is inconsistent with this specification, the specification will supersede any such material.